Saturday, June 21, 2014

Hydra v3.1 a success

The Hydra v3.1 boards came back from OSHPark, and they're a success. Since they had both the new DC-DC converter circuitry for the +5 and -12 supply, and the new 4 transistor pilot generator circuitry, it was quite a risk, since both are fairly critical subsystems and both were completely untested.

The power supplies work perfectly. The pilot generator works, but there is one little caveat - If you attempt to program the controller while 12 volt power is present, the TTL pilot output line will float, which will wind up turning both transistors on, shorting +12 to -12. The workaround is to not program the controller with power applied, but the fix is to add a pull-up resistor to insure that the floating bases aren't allowed. That will be the design going forward for both OpenEVSE II and the Hydra.

Hydra v3.2's design is well underway. It's going to be a two-board system, like OpenEVSE II. It's going to have an inter-board FFC cable. The mezzanine board has all of the AC systems - the 12 volt power supply, 2 contractor triac circuits, and two MID400 AC testers. The top board is the logic/display board that it more or less always has been. Going forward, I'm dropping support for 12 volt relay coils. DigiKey has 208/240 volt coil 30A contactors with the same form factor. It's not going to support L1 (120v) charging anymore, but nobody in their right mind would build a Hydra for L1 anyway.

Meanwhile, the OpenEVSE II display/logic board prototypes have been ordered. The prototype HV boards should arrive this week.